Rear subframe structure

ABSTRACT

A rear subframe structure is provided with a rear subframe including a front cross member, and a pair of left and right side members connected to the front cross member, and further including a vehicle-body mounting portion formed on both ends of the front cross member. The rear subframe includes a tunnel portion formed in a middle of a lower portion of the front cross member, and a brace extending in the vehicle width direction, and including a tunnel-portion mounting portion on left and right ends thereof. The brace includes a middle downwardly bulging portion bulging downwardly, and an upwardly bulging portion continued outwardly of the middle downwardly bulging portion and bulging upwardly. An inflection point between the middle downwardly bulging portion and the upwardly bulging portion is substantially located on an imaginary line linearly connecting the left and right tunnel-portion mounting portions in the vehicle width direction.

TECHNICAL FIELD

The present invention relates to a rear subframe structure of a vehicle, and more particularly, to a rear subframe structure provided with a rear subframe including a front cross member extending in a vehicle width direction, and a pair of left and right side members connected to the front cross member and extending in a vehicle front-rear direction; and a vehicle-body mounting portion formed on both ends of the front cross member in the vehicle width direction.

BACKGROUND ART

Generally, a rear subframe is configured such that a pair of front and rear cross members extending in a vehicle width direction, and left and right side members extending in a vehicle front-rear direction are connected substantially in a grid pattern in a plan view of a vehicle.

In a case where the aforementioned rear subframe is mounted on a vehicle configured such that the height of a rear seat pan is set low in order to secure comfort of a passenger seated on a rear seat and to secure a low hip point, a portion above a front-side vehicle-body mounting portion of the rear subframe is restricted by the rear seat pan. Furthermore, it is necessary to dispose a propeller shaft and an exhaust pipe in the vehicle front-rear direction. Therefore, a front cross member constituting the rear subframe may be formed into a saddle shape.

In order to reinforce a lower portion of the saddle-shaped front cross member, it is proposed to dispose a brace below the saddle-shaped portion in the vehicle width direction. However, there is a problem that it is difficult to dispose a thick brace in a straight manner in the vehicle width direction in a case where an exhaust pipe and a propeller shaft are disposed in a narrow space restricted by the rear seat pan.

Patent Literature 1 discloses a configuration, in which an upper member element corresponding to a rear subframe is provided, a saddle-shaped portion for receiving a propeller shaft in a vehicle front-rear direction is formed on the upper member element, and a lower member element corresponding to a brace is provided below the saddle-shaped member.

However, in the conventional structure disclosed in Patent Literature 1, in view of a point that the aforementioned lower member element is formed substantially linearly in the vehicle width direction in a front view, there is a problem that the layout of an exhaust pipe is deteriorated in a case where the aforementioned conventional structure is employed in a vehicle configured such that the height of a rear seat pan is set low. Thus, there is room for improvement.

CITATION LIST Patent Literature

-   Patent Literature 1: U.S. Pat. No. 5,833,026

SUMMARY OF INVENTION

In view of the above, an object of the present invention is to provide a rear subframe structure which enables to secure a substantially linear load transmission path in a vehicle width direction while avoiding a propeller shaft and an exhaust pipe, and to reinforce a front cross member even in a portion where it is difficult to dispose a thick brace in a straight manner in the vehicle width direction.

An aspect of the present invention is directed to a rear subframe structure provided with a rear subframe including a front cross member extending in a vehicle width direction, and a pair of left and right side members connected to the front cross member and extending in a vehicle front-rear direction; a vehicle-body mounting portion formed on both ends of the front cross member in the vehicle width direction; a tunnel portion formed in a middle of a lower portion of the front cross member through which a propeller shaft extends; and a brace extending in the vehicle width direction below the tunnel portion, and including a tunnel-portion mounting portion on left and right ends thereof. The brace includes a middle downwardly bulging portion bulging downwardly while avoiding the propeller shaft, and an upwardly bulging portion continued outwardly of the middle downwardly bulging portion in the vehicle width direction and bulging upwardly while avoiding an exhaust pipe. An inflection point between the middle downwardly bulging portion and the upwardly bulging portion is substantially located on an imaginary line linearly connecting the left and right tunnel-portion mounting portions in the vehicle width direction.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a rear subframe structure according to the present invention;

FIG. 2 is a plan view of the rear subframe structure;

FIG. 3 is a bottom view of the rear subframe structure;

FIG. 4 is a front view of the rear subframe structure;

FIG. 5 is a rear view of the rear subframe structure;

FIG. 6 is a perspective view of the rear subframe structure when viewed from rear on a vehicle left side;

FIG. 7 is a perspective view of the rear subframe structure when viewed from rear and above on a vehicle right side;

FIG. 8A is a sectional view taken along the line A-A in FIG. 2;

FIG. 8B is a sectional view taken alone the line B-B in FIG. 2;

FIG. 9 is a sectional view taken along the line C-C in FIG. 2;

FIG. 10 is a side view illustrating essential parts of FIG. 2;

FIG. 11 is a sectional view taken along the line D-D in FIG. 10;

FIG. 12A is a plan view of a partition member;

FIG. 12B is a perspective view of the partition member;

FIG. 13A is a perspective view of a stabilizer support member; and

FIG. 13B is a front view of a brace.

DESCRIPTION OF EMBODIMENTS

In the following, an embodiment of the present invention is described in detail based on the drawings.

FIG. 1 is a perspective view of a rear subframe structure, FIG. 2 is a plan view of the rear subframe structure, FIG. 3 is a bottom view of the rear subframe structure, FIG. 4 is a front view of the rear subframe structure, and FIG. 5 is a rear view of the rear subframe structure. In FIG. 1, the arrow F indicates a vehicle front side, the arrow R indicates a vehicle rear side, the arrow IN indicates an inner side in a vehicle width direction, and the arrow OUT indicates an outer side in a vehicle width direction (the same definition is also applied to the other drawings).

Referring to FIG. 1 to FIG. 5, a rear subframe 10 for supporting a rear suspension includes a front cross member 11 extending in the vehicle width direction on the front side, a rear cross member 12 extending in the vehicle width direction on the rear side of the front cross member 11, a pair of upper side members 13 and 13 for connecting the front cross member 11 and the rear cross member 12 in a vehicle front-rear direction, and a pair of lower side members 14 and 14 for connecting the front cross member 11 and the rear cross member 12 in the vehicle front-rear direction. These members are connected substantially in a grid pattern in a plan view of a vehicle. Each of the members 11 to 14 has a closed sectional structure.

In the embodiment, the upper side member 13 is connected to a lateral portion of the front cross member 11 in the vehicle width direction via a pillar portion 33 (see FIG. 10) to be described later, and extends from the connection portion rearwardly of a vehicle.

Further, the rear cross member 12 connects rear portions of the paired left and right upper side members 13 and 13 in the vehicle width direction, connects rear portions of the paired left and right lower side members 14 and 14 in the vehicle width direction, and further connects the upper and lower side members 13 and 14 in an up-down direction.

As illustrated in FIG. 2, the lower side member 14 is located on the inner side than the upper side member 13 in the vehicle width direction, and connects a lower portion of the front cross member 11 and a lower portion of the rear cross member 12 in the vehicle front-rear direction.

As illustrated in FIG. 2 and FIG. 3, a distance between rear ends of the paired left and right lower side members 14 and 14 is set smaller than a distance between front ends of the paired left and right lower side members 14 and 14. Thereby, lower-arm rear-side support portions 12 b and 12 c (see FIG. 6) to be described later are formed at positions where the lower-arm rear-side support portions 12 b and 12 c overlap the upper side member 13 in a plan view.

As illustrated in FIG. 1 to FIG. 5, front-side vehicle-body mounting portions 15 and 15 are formed on both ends of the front cross member 11 in the vehicle width direction. A rear portion of the upper side member 13 is smoothly formed into a curve rearwardly of the vehicle and outwardly in the vehicle width direction. Rear-side vehicle-body mounting portions 16 and 16 are formed on rear ends of the upper side members 13 and 13. The rear subframe 10 is mounted to a vehicle body, specifically, to a rear side frame via the vehicle-body mounting portions 15 and 16.

The reference numeral 17 denotes a lower arm. A link support portion 17 a is formed on a front portion of an outer end of the lower arm 17 in the vehicle width direction. A lower end of an integral link 18 is pivotally supported on the link support portion 17 a. An upper end of the integral link 18 is pivotally connected to an integral link support portion of a hub support 19.

The integral link 18 is a link for controlling a recession angle (an angle defined by a road surface, and a swing trajectory of a rear wheel in a side view when the rear wheel moves up and down in a case where the rear wheel rides on a step).

In the embodiment, an H-shaped lower arm is employed as the lower arm 17. A connection portion 17 b is formed on a rear portion of an outer end of the lower arm 17 in the vehicle width direction (see FIG. 3). The connection portion 17 b is pivotally connected to a lower-arm support portion of the hub support 19.

The reference numeral 20 denotes a toe control link for setting a rear wheel to toe-in so as to secure wheel straightness. A connection portion 20 a is formed on an outer end of the toe control link 20 in the vehicle width direction. The connection portion 20 a is pivotally connected to a toe control link support portion of the hub support 19.

The reference numeral 21 denotes an upper arm. A connection portion 21 a is formed on an outer end of the upper arm 21 in the vehicle width direction. The connection portion 21 a is pivotally connected to an upper-arm support portion of the hub support 19. In the embodiment, an I-shaped upper arm is employed as the upper arm 21.

As illustrated in FIG. 1, FIG. 4, and FIG. 5, a damper support portion 19 a extending inwardly in the vehicle width direction is integrally formed on the hub support 19. A damper 22 of a strut structure is mounted on the damper support portion 19 a.

As illustrated in FIG. 2 and FIG. 3, a bulging portion 17 c bulging rearwardly is formed on a rear portion of the lower arm 17. A coil spring 24 is wound between a spring lower retainer 23 mounted on an upper portion of the bulging portion 17 c, and a spring upper retainer (not illustrated) provided on the rear side frame on the vehicle body side.

As illustrated in FIG. 2, FIG. 3, and FIG. 5, a stabilizer 25 is provided on the rear side of the rear cross member 12 along the rear cross member 12. The stabilizer 25 is formed into a bent shape forwardly of a vehicle in such a manner that left and right ends of the stabilizer 25 are located above the lower arm 17. The bent ends of the stabilizer 25 are connected to the lower arm 17 by using a connection member. The stabilizer 25 is configured to suppress a roll angle when one wheel is bumped or rebound by torsional rigidity resistance.

As illustrated in FIG. 4, a tunnel portion 11 a for receiving a propeller shaft 26 in the vehicle front-rear direction is formed in the middle of a lower portion of the front cross member 11. The front cross member 11 is formed into a saddle shape. Further, a brace 27 as a reinforcement member for connecting lower portions of the tunnel portions 11 a in the vehicle width direction is provided.

As illustrated in FIG. 1 to FIG. 3, a differential mount portion 12 a is formed on an intermediate portion of the rear cross member 12 in the vehicle width direction. A differential mount bracket 29 is mounted on the differential mount portion 12 a via a differential mount bush 28.

A vehicle in the embodiment is a vehicle of a type such that a driving force is transmitted to rear wheels. The vehicle is configured such that a rear portion of a rear differential device (not illustrated) is supported by the differential mount bracket 29.

FIG. 6 is a perspective view of the rear subframe structure when viewed from rear on a vehicle left side, FIG. 7 is a perspective view of the rear subframe structure when viewed from rear and above on a vehicle right side, FIG. 8A is a sectional view taken along the line A-A in FIG. 2, FIG. 8B is a sectional view taken along the line B-B in FIG. 2, FIG. 9 is a sectional view taken along the line C-C in FIG. 2, FIG. 10 is a side view illustrating essential parts of FIG. 2, and FIG. 11 is a sectional view taken along the line D-D in FIG. 10.

FIG. 6 to FIG. 11 illustrate a configuration of a vehicle left side portion. The configuration of a vehicle right side portion is symmetrical or substantially symmetrical with respect to the configuration of the vehicle left side portion in a left-right direction.

As illustrated in FIG. 8A, FIG. 8B, FIG. 9, and FIG. 11, the front cross member 11 has a structure such that a front panel 31 located on the front side and a rear panel 32 located on the rear side are joined and fixed, and has a closed section S1 extending in the vehicle width direction. Specifically, the closed section S1 is constituted by the rear panel 32 on the middle side (specifically, on the rear side) of the rear subframe 10, and the front panel 31 including an upper surface 31 a extending rearwardly than the rear panel 32 and including a front surface 31 b extending downwardly than the rear panel 32.

As illustrated in FIG. 1 and FIG. 6, left and right lateral portions of the front cross member 11 are inclined outwardly in the vehicle width direction, and forwardly and downwardly. Thereby, as illustrated in FIG. 8B and FIG. 9, a front portion of the closed section S1 extends downwardly to form an enlarged closed section S1 a. Further, as illustrated in FIG. 8B and FIG. 9, a rear portion of the closed section S1 on a lateral portion of the front cross member 11 in the vehicle width direction is projected upwardly and rearwardly to form a recessed closed section S1 b. The enlarged closed section S1 a and the recessed closed section S1 b are continued.

As illustrated in FIG. 6, FIG. 8B, and FIG. 9, there is formed, on a rear portion of the enlarged closed section S1 a, a lower-arm support portion 32 a for supporting a front mounting portion 17 d out of front and rear mounting portions 17 d and 17 e of the lower arm 17.

As illustrated in FIG. 8B, the upper side member 13 is connected to a rear surface of an upper portion of the closed section S1, specifically, to a rear surface of the recessed closed section S1 b via the pillar portion 33.

As described above, by inclining a lateral portion of the front cross member 11 in the vehicle width direction forwardly and downwardly, it is possible to enlarge a front portion of the closed section S1 downwardly (see the enlarged closed section S1 a), while avoiding interference with a rear seat pan (a rear floor panel), whereby rigidity in the vehicle width direction is secured without narrowing a swing range of the lower arm 17.

In other words, even in a structure configured such that the rear subframe 10 is disposed in a narrow space of a lower portion of a rear seat pan where it is not possible to connect the front cross member 11 and the upper side member 13, while securing a sufficient closed sectional structure (a linearly extending closed sectional structure), it is possible to secure high rigidity in the vehicle width direction, and to secure a space for the lower-arm support portion 32 a (specifically, secure a space for the mounting portion 17 d of the lower arm 17).

As illustrated in FIG. 6, FIG. 7, and FIG. 8B, the pillar portion 33 has a shape of a closed section S2 constituted by a rear plate 34 including an upper-arm support portion 34 a for supporting a mounting portion 21 b (see FIG. 2) of the upper arm 21, and a front plate 35 including a lower-arm support portion 35 a. As illustrated in FIG. 6 and FIG. 11, the rear plate 34 is formed to have a U-shaped section in a plan view.

As illustrated in FIG. 7, the front plate 35 includes a dome-shaped flange portion 35 b which extends from an outer peripheral edge of a main surface portion thereof forwardly of the vehicle, and which is abutted against a back surface of the rear panel 32 of the front cross member 11 and welded.

As illustrated in FIG. 8B and FIG. 9, a second closed section S3 extending in the vehicle width direction is constituted by the closed section S1 of a lateral portion of the front cross member 11 in the vehicle width direction, the front plate 35 located immediately on the rear side of the closed section S1, and an upper surface of the lower side member 14. Thereby, a space for supporting a lower arm is secured, and connection rigidity of the lower side member 14 is enhanced.

As illustrated in FIG. 7, a lower portion of the front plate 35 is fixed by abutment against an upper surface of the lower side member 14 and against an outer lateral surface of the lower side member 14 in the vehicle width direction and by welding.

As illustrated in FIG. 8B, the pillar portion 33 having a structure of the closed section S2 is formed immediately on the rear side of the second closed section S3. The pillar portion 33 includes the front plate 35, extends upwardly from the lower side member 14, and is connected to a back surface of the front cross member 11. A rear surface of an upper portion of the pillar portion 33, specifically, a rear surface of an upper portion of the rear plate 34 is connected to a front portion of the upper side member 13 by welding.

In other words, the front-side lower-arm support portion 32 a out of the lower-arm support portions 32 a and 35 a is formed by a part (a part of the enlarged closed section S1 a) configured such that a front portion of the closed section S1 extends downwardly out of a lateral portion of the front cross member 11 in the vehicle width direction, and the rear-side lower-arm support portion 35 a is formed by the pillar portion 33 having a structure of the closed section S2. Further, the pillar portion 33 is connected to all of the upper side member 13, the lower side member 14, and the front cross member 11. According to this configuration, it is possible to distribute load to be input via the lower-arm support portions 32 a and 35 a, and to attain high rigidity of the rear subframe 10.

Further, in order to secure a sufficient space for supporting a lower arm while lowering a lateral portion of the front cross member 11 in the vehicle width direction, the pillar portion 33 (specifically, the rear plate 34) is used as a set plate, while reducing the size of the recessed closed section S1 b in the up-down direction than the size of the upper side member 13 in the up-down direction, whereby connection rigidity is enhanced.

As illustrated in FIG. 6, FIG. 7, and FIG. 8B, the vertical-wall-shaped pillar portion 33 constituted by the front plate 35 and the rear plate 34, and extending in the vehicle width direction and in the up-down direction is held and fixed between a lateral portion of the front cross member 11 in the vehicle width direction, and a front end of the upper side member 13.

As illustrated in FIG. 6, FIG. 7, and FIG. 8B, a lower portion of the pillar portion 33, specifically, lower portions of the front plate 35 and the rear plate 34 are respectively connected to an upper surface of the lower side member 14 and to an outer lateral surface of the lower side member 14 in the vehicle width direction. The upper-arm support portion 34 a is formed on an upper portion of the rear plate 34, and the lower-arm support portion 35 a is formed on a lower portion of the front plate 35.

According to the aforementioned configuration, load input from the upper and lower arms (the lower arm 17 and the upper arm 21) is directly transmitted to the upper and lower side members 13 and 14 and to the front cross member 11 for load distribution, whereby high rigidity of the rear subframe 10 is attained. Further, the upper and lower arm support portions 34 a and 35 a are formed on the pillar portion 33. This makes it possible to enhance positioning accuracy between the lower arm 17 and the upper arm 21.

As illustrated in FIG. 6, FIG. 7, and FIG. 10, the upper-arm support portion 34 a includes a substantially Z-shaped upper-arm support bracket 36 on a rear portion thereof in a side view.

The upper-arm support bracket 36 includes a vertical piece 36 a extending in the up-down direction, an upper piece 36 b extending rearwardly from an upper end of the vertical piece 36 a, and a lower piece 36 c extending forwardly from a lower end of the vertical piece 36 a. The upper-arm support bracket 36 is integrally formed by these pieces 36 a to 36 c. As illustrated in FIG. 10, an upper half of the vertical piece 36 a and the upper piece 36 b are abutted against an outer lateral surface of the upper side member 13 in the vehicle width direction and welded, and a front end of the lower piece 36 c is abutted against a back surface of the rear plate 34 and welded.

As illustrated in FIG. 10, the upper-arm support bracket 36 holds the pillar portion 33 in cooperation with the front cross member 11. Further, a front portion of the upper side member 13 and the pillar portion 33 are connected by the upper-arm support bracket 36. By the aforementioned holding structure of the pillar portion 33 by the upper-arm support bracket 36 and the front cross member 11, the pillar portion 33 is securely supported, and the upper arm 21 is supported by the upper-arm support portion 34 a on the upper portion of the pillar portion 33 and the upper-arm support bracket 36, whereby support rigidity of the upper arm 21 is enhanced. Further, connection rigidity between the pillar portion 33 and the upper side member 13 is enhanced.

As illustrated in FIG. 8B, an upper portion of the rear plate 34 of the pillar portion 33 is directly connected to the front cross member 11 (specifically, a rear portion of the upper surface 31 a of the front panel 31), and the lower-arm support portions 35 a and 32 a are constituted by a lower portion of the front plate 35 and a lower portion of the front cross member 11 (specifically, a lower portion of the rear panel 32). Thus, load from the upper arm 21 and the lower arm 17 is transmitted to the front cross member 11 and to the upper and lower side members 13 and 14 for load distribution, and high rigidity of the rear subframe 10 is attained.

As illustrated in FIG. 8B and FIG. 10, the pillar portion 33 extends in the up-down direction between the upper side member 13 and the lower side member 14, and the lower-arm support portion 35 a is formed on a front surface of the pillar portion 33 on an upper side of the lower side member 14, in other words, on the front plate 35.

Further, as illustrated in FIG. 6, FIG. 7, and FIG. 8B, a toe control link support portion 34 b is formed on a rear surface of the pillar portion 33 located below the lower-arm support portion 35 a, and on an outer lateral side of the lower side member 14 in the vehicle width direction, in other words, on the rear plate 34.

As illustrated in FIG. 6, FIG. 7, and FIG. 11, a toe control link support bracket 37 (hereinafter, simply referred to as a link support bracket) for supporting the toe control link support portion 34 b from the rear side is provided on the rear subframe 10.

As illustrated in FIG. 6, FIG. 7, and FIG. 11, the link support bracket 37 includes a front piece 37 a fixed upright on an upper surface of the lower side member 14 and extending in the vehicle front-rear direction, and a lateral piece 37 c extending from a rear end of the front piece 37 a outwardly in the vehicle width direction. The link support bracket 37 is integrally formed by these pieces 37 a and 37 b. A horizontally U-shaped cutaway portion 37 b is formed in the lateral piece 37 c. The cutaway portion 37 b of the lateral piece 37 c is welded and fixed to an upper surface, an outer lateral surface, and a lower surface of the lower side member 14.

Further, the link support bracket 37 is mounted between the lower side member 14 and a back surface of the lower-arm support portion 35 a of the pillar portion 33.

The lower-arm support portion 35 a and the toe control link support portion 34 b are displaced in the up-down direction. Thereby, a compact and dense layout by the support portions 35 a and 34 b, the lower arm 17, and the toe control link 20 is obtained. Further, load from the lower arm 17 and the toe control link 20 is distributed to an upper surface and a lateral surface of the lower side member 14, and further to the upper and lower side members 13 and 14, whereby high rigidity of the rear subframe 10 is attained. In addition to the above, the pillar portion 33 supports two components i.e. the lower arm 17 and the toe control link 20 to enhance positioning accuracy between the lower arm 17 and the toe control link 20.

The lower-arm support portion 35 a for supporting the lower arm 17 is formed as a first arm support portion. Therefore, it is possible to offset the front mounting portion 17 d of the lower arm 17 to the inner side in the vehicle width direction than an outer lateral edge of the lower side member 14 in the vehicle width direction. Thus, it is possible to enhance freedom in setting an imaginary lower-arm swing centerline L illustrated in FIG. 8B.

As illustrated in FIG. 8B, the vehicle-body mounting portions 17 d and 17 e are formed on front and rear portions of the lower arm 17 to be supported by the lower-arm support portion 35 a. Specifically, the lower arm 17 includes the front mounting portion 17 d on the front side with respect to the pivot center of the lower arm 17, and the rear mounting portion 17 e on the rear side with respect to the pivot center of the lower arm 17.

Further, the lower-arm rear-side support portions 12 b and 12 c connected to the rear cross member 12 or integrally formed with the rear cross member 12 are formed such that the lower-arm swing centerline L located on the lower side than the lower-arm support portion 35 a of the pillar portion 33 and passing through the front and rear mounting portions 17 d and 17 e of the lower arm 17 is located on the upper side than the link support portion 34 b.

As illustrated in FIG. 8B, the upper and lower side members 13 and 14 are connected by the rear cross member 12 in the up-down direction, and form a rigid box-shaped structure. Further, the rear-side support portions 12 b and 12 c of the lower arm 17 are formed on a lower portion of the rear cross member 12 to distribute load of the lower arm 17 in the front-rear direction via the front and rear mounting portions 17 d and 17 e. Further, the lower-arm swing centerline L (an imaginary axis) is formed on the upper side than the link support portion 34 b with an angle at which the front and rear mounting portions 17 d and 17 e of the lower arm 17 obtain a recession angle. Thereby, even in a narrow space such that the rear seat pan comes close, it is possible to rigidly form the lower-arm front-side support portion 35 a and the link support portion 34 b.

Specifically, it is possible to avoid interference with the toe control link 20, while enhancing support rigidity by a support portion of the lower arm 17, whereby it is easy to set a recession angle.

As illustrated in FIG. 9 and FIG. 10, the rear cross member 12 for connecting the upper side member 13 and the lower side member 14 in the up-down direction has a structure of a closed section S4 of a T-shape in a side view, whose size is increased in the vehicle front-rear direction along an inner lateral surface of the upper side member 13 in the vehicle width direction (in other words, an inner hollow structure of a T-shape in a side view).

As illustrated in FIG. 1 and FIG. 2, the closed section S4 of a T-shape in a side view is formed only on left and right side portions of the rear cross member 12. As illustrated in FIG. 8A, a closed section S5 extending in the up-down direction and having an I-shape in a side view is formed on an intermediate portion of the rear cross member 12 in the vehicle width direction. The closed sections S4 and S5 communicate with each other.

Further, as illustrated in FIG. 9, the lower-arm rear-side support portions 12 b and 12 c are formed on the lower side of a lateral portion of the rear cross member 12 in the vehicle width direction, which is associated with the closed section S4 of a T-shape in a side view; and the rear mounting portion 17 e of the lower arm 17 is supported by the lower-arm rear-side support portions 12 b and 12 c.

The rear cross member 12 including the closed section S4 of a T-shape in a side view includes, on an upper portion thereof, an upper-surface front-side projection portion 12 d and an upper-surface rear-side projection portion 12 e bulging in the vehicle front-rear direction. A stabilizer support bracket 38 is mounted between the upper-surface rear-side projection portion 12 e, and the rear-side lower-arm rear-side support portion 12 c (in this embodiment, near the rear-side lower-arm rear-side support portion 12 c) out of the paired front-side and rear-side lower-arm rear-side support portions 12 b and 12 c.

As described above, forming the rear cross member 12 into a structure of the closed section S4 of a T-shape in a side view makes it possible to increase the size of a closed section of the rear cross member 12 and to enhance rigidity. Further, mounting the stabilizer support bracket 38 between the upper-surface rear-side projection portion 12 e and the lower-arm support portion 12 c of the rear cross member 12 makes it possible to reinforce the rear cross member 12 by the stabilizer support bracket 38, and to secure a space for installing the stabilizer 25 without increasing the number of parts.

FIG. 13A is a perspective view illustrating the stabilizer support bracket 38. As illustrated in FIG. 13A, the stabilizer support bracket 38 is integrally formed by a pair of inner and outer lateral pieces 38 a and 38 b in the vehicle width direction, and a rear piece 38 c for connecting the lateral pieces 38 a and 38 b. The rear piece 38 c is inclined in a state that a front portion thereof is inclined downwardly and a rear portion thereof is inclined upwardly when assembling the stabilizer support bracket 38 to the rear subframe 10 (specifically, the rear cross member 12) is completed.

The stabilizer 25 is mounted to a back surface of the rear piece 38 c of the stabilizer support bracket 38 with use of a support bracket 39, which is fastened by a bolt and a nut (see FIG. 6 and FIG. 9).

As illustrated in FIG. 1 and FIG. 2, there are formed, on a top portion of the rear cross member 12, a ridge X1 extending in the vehicle width direction on an intermediate portion thereof in the vehicle width direction, ridges X2 and X2 extending outwardly in the vehicle width direction from left and right ends of the ridge X1 along an upper end of a front portion of the upper-surface front-side projection portion 12 d, and ridges X3 and X3 extending outwardly in the vehicle width direction from connection portions of the ridges X1 and X2 along an upper end of a rear portion of the upper-surface rear-side projection portion 12 e. The ridges X1, X2, and X3 are combined substantially in an X-shape in a plan view. Thereby, torsional rigidity of the rear cross member 12 is enhanced.

As illustrated in FIG. 9 and FIG. 10, a partition member 40 is provided within the closed section S4 in the vicinity of a lower end of the stabilizer support bracket 38 of the rear cross member 12. A lower-portion closed section S6 extending in the vehicle width direction is formed by the partition member 40 and an upper surface of the lower side member 14.

Forming the lower-portion closed section S6 makes it possible to enhance local rigidity of the rear cross member 12 in the vehicle width direction, to increase load transmission from the lower-arm rear-side support portions 12 b and 12 c, to prevent sectional deformation by concentration of stress, and to enhance rigidity in the vehicle width direction.

FIG. 12A is a plan view of the partition member 40, and FIG. 12B is a perspective view of the partition member 40. The partition member 40 includes a lower piece 40 a located within the closed section S4 of the rear cross member 12 and extending in the vehicle width direction, and a lateral piece 40 b extending from an outer end of the lower piece 40 a in the vehicle width direction upwardly by a predetermined amount corresponding to a width of the rear cross member 12 in the front-rear direction, and then, whose sizes of front and rear portions are increased. The partition member 40 is integrally formed by these pieces 40 a and 40 b. As illustrated in FIG. 11, the lower piece 40 a is welded and fixed to front and rear walls of the rear cross member 12. As illustrated in FIG. 9, an upper end of the lateral piece 40 b is welded and fixed to a lower surface of the upper-surface front-side projection portion 12 d and to a lower surface of the upper-surface rear-side projection portion 12 e. The rear cross member 12 may be formed by combining two members, or may be formed by a hydroformed component.

FIG. 13B is a front view enlargedly illustrating the brace 27. As illustrated in FIG. 4 and FIG. 13B, the brace 27 includes a middle downwardly bulging portion 27 a bulging downwardly while avoiding the propeller shaft 26, and a pair of left and right upwardly bulging portions 27 b and 27 b bulging upwardly on left and right outer sides of the middle downwardly bulging portion 27 a in the vehicle width direction while avoiding an exhaust pipe 41 (the exhaust pipe 41 is provided only on the vehicle right side). The brace 27 is integrally formed by these portions. In this embodiment, the brace 27 is constituted by an aluminum die cast member.

As illustrated in FIG. 13B, the middle downwardly bulging portion 27 a, and the upwardly bulging portions 27 b and 27 b on the left and right sides of the middle downwardly bulging portion 27 a are smoothly and integrally connected.

As illustrated in FIG. 3, tunnel-portion mounting portions 27 c and 27 c (hereinafter, simply referred to as mounting portions) extending rearwardly up to the positions of the vehicle-body mounting portions of the toe control link 20 are integrally formed on lateral portions of the brace 27 in the vehicle width direction.

Further, the brace 27 is formed in such a manner that an inflection point between the middle downwardly bulging portion 27 a and the upwardly bulging portion 27 b is substantially located on an imaginary line linearly connecting the left and right tunnel-portion mounting portions 27 c and 27 c in the vehicle width direction. According to this configuration, as illustrated in FIG. 13B, a load transmission path 50 for substantially linearly connecting the left and right mounting portions 27 c and 27 c in the vehicle width direction is formed in the brace 27.

Specifically, preferably, an edge of a bulging portion on the non-bulging side may be proximate to an imaginary line passing though the left and right mounting portions 27 c and 27 c as illustrated in FIG. 13B, and more preferably, the edge may overlap the imaginary line. Further, in a case where the edge is proximate to the imaginary line without overlapping, preferably, the bending amount of the edge on the non-bulging side with respect to the imaginary line may be smaller than the bending amount of the edge on the bulging side, specifically, the distance of the edge on the non-bulging side from the imaginary line may be small, and the edge on the non-bulging side may have a shape approximate to a straight line.

According to the aforementioned configuration, even in a portion where it is difficult to dispose a thick brace in a straight manner in the vehicle width direction, it is possible to secure the load transmission path 50 for linearly connecting the left and right mounting portions 27 c and 27 c of the brace 27 in the vehicle width direction, while avoiding the propeller shaft 26 and the exhaust pipe 41, and to reinforce the brace 27 itself by the bulging portions 27 a and 27 b to thereby reinforce the front cross member 11.

As illustrated in FIG. 4 and FIG. 13B, a differential mount portion 27 d for supporting a differential mount bush 42 is provided for each of the paired left and right upwardly bulging portions 27 b of the brace 27. This enables to reinforce the differential mount portion 27 d by the upwardly bulging portion 27 b, and to support a rear differential device (not illustrated) without increasing the number of parts. Thus, it is not necessary to additionally provide a differential mount bracket on the front side of the rear differential device.

As illustrated in FIG. 2, a rear differential device (not illustrated) is supported by the differential mount bush 42, and by the rear-side differential mount bracket 29 located on the rear side of the differential mount bush 42.

As illustrated in FIG. 3 and FIG. 8B, the brace 27 is connected to the lower side member 14 at a position where the brace 27 overlaps, in a bottom view, the lower-arm support portions 32 a and 35 a constituted by a lower portion of the front cross member 11, and the pillar portion 33 formed on the rear side of the lower portion of the front cross member 11.

Specifically, the mounting portion 27 c of the brace 27 is connected and fixed to a bottom surface of the lower side member 14 so as to overlap the lower-arm support portions 32 a and 35 a in a bottom view with use of a plurality of fastening members 43 and 43 such as bolts at a position away from the mounting portion 27 c in the front-rear direction. Thus, the lower-arm support portions 32 a and 35 a are reinforced with use of the brace 27.

In FIG. 1 and FIG. 5, the reference numeral 44 denotes an opening portion for weight reduction. In FIG. 6 and FIG. 7, the reference numeral 45 denotes an opening portion for use in mounting the mounting portion 17 d of the lower arm 17. In FIG. 8A, the reference numeral 46 denotes an arc-shaped recess portion for avoiding interference with a spare tire pan.

As described above, the rear subframe structure of the embodiment is a rear subframe structure provided with the rear subframe 10 including the front cross member 11 extending in the vehicle width direction, and a pair of left and right side members (see the upper side members 13 and 13) connected to the front cross member 11 and extending in the vehicle front-rear direction; the vehicle-body mounting portions 15 and 15 formed on both ends of the front cross member 11 in the vehicle width direction; the tunnel portion 11 a formed in the middle of a lower portion of the front cross member 11 through which the propeller shaft 26 extends; and the brace 27 for connecting a lower portion of the tunnel portion 11 a in the vehicle width direction. The brace 27 includes the middle downwardly bulging portion 27 a bulging downwardly while avoiding the propeller shaft 26, and the upwardly bulging portion 27 b bulging upwardly on the outer side of the middle downwardly bulging portion 27 a in the vehicle width direction while avoiding the exhaust pipe 41. The brace 27 includes the load transmission path 50 for substantially linearly connecting the left and right mounting portions 27 c and 27 c in the vehicle width direction (see FIG. 1, FIG. 4, and FIG. 13B).

According to the aforementioned configuration, even in a portion where it is difficult to dispose a thick brace in a straight manner in the vehicle width direction, it is possible to secure the load transmission path 50 for linearly connecting the left and right mounting portions 27 c and 27 c of the brace 27 in the vehicle width direction, while avoiding the propeller shaft 26 and the exhaust pipe 41, and to reinforce the brace 27 itself by the bulging portions 27 a and 27 b to thereby reinforce the front cross member 11.

In the embodiment of the present invention, the differential mount portion 27 d for supporting the differential mount bush 42 is formed on the upwardly bulging portion 27 b (see FIG. 4 and FIG. 13B).

According to the aforementioned configuration, it is possible to reinforce the differential mount portion 27 d by the upwardly bulging portion 27 b, and to support a rear differential device, without increasing the number of parts. Further, it is not necessary to additionally provide a differential mount bracket.

In the embodiment of the present invention, the rear subframe 10 further includes the rear cross member 12 extending in the vehicle width direction on a rear side of the front cross member 11, and the lower side member 14 extending in the vehicle front-rear direction on a lower side of the side member (the upper side member 13). The brace 27 is connected to the lower side member 14 at a position where the brace 27 overlaps, in a bottom view, the lower-arm support portions 32 a and 35 a constituted by the lower portion of the front cross member 11, and the pillar portion 33 formed on a rear side of the lower portion of the front cross member 11 between an upper portion of the front cross member 11 and the lower side member 14, or between the side member (in other words, the upper side member 13) and the lower side member 14 (see FIG. 3 and FIG. 8B).

According to the aforementioned configuration, it is possible to reinforce the lower-arm support portions 32 a and 35 a themselves by the brace 27.

The following is a summary of the present invention as described above.

A rear subframe structure according to the present invention is a rear subframe structure provided with a rear subframe including a front cross member extending in a vehicle width direction, and a pair of left and right side members connected to the front cross member and extending in a vehicle front-rear direction; a vehicle-body mounting portion formed on both ends of the front cross member in the vehicle width direction; a tunnel portion formed in a middle of a lower portion of the front cross member through which a propeller shaft extends; and a brace extending in the vehicle width direction below the tunnel portion, and including a tunnel-portion mounting portion on left and right ends thereof. The brace includes a middle downwardly bulging portion bulging downwardly while avoiding the propeller shaft, and an upwardly bulging portion continued outwardly of the middle downwardly bulging portion in the vehicle width direction and bulging upwardly while avoiding an exhaust pipe. An inflection point between the middle downwardly bulging portion and the upwardly bulging portion is substantially located on an imaginary line linearly connecting the left and right tunnel-portion mounting portions in the vehicle width direction.

According to the aforementioned configuration, even in a portion where it is difficult to dispose a thick brace in a straight manner in the vehicle width direction, it is possible to secure a load transmission path for substantially linearly connecting the left and right tunnel-portion mounting portions of the brace in the vehicle width direction, while avoiding the propeller shaft and the exhaust pipe, and to reinforce the brace itself by the bulging portions to thereby reinforce the front cross member.

In an aspect of the present invention, a differential mount portion for supporting a differential mount bush may be formed on the upwardly bulging portion.

According to the aforementioned configuration, it is possible to reinforce the differential mount portion by the bulging portion, and to support a rear differential device without increasing the number of parts. Further, it is not necessary to additionally provide a differential mount bracket.

In an aspect of the present invention, when it is assumed that the side member is an upper side member, the rear subframe may further include a rear cross member extending in the vehicle width direction on a rear side of the front cross member, and a lower side member extending in the vehicle front-rear direction on a lower side of the upper side member. The brace is connected to the lower side member at a position where the brace overlaps, in a bottom view, a lower-arm support portion constituted by the lower portion of the front cross member, and a pillar portion formed on a rear side of the lower portion of the front cross member between an upper portion of the front cross member and the lower side member, or between the upper side member and the lower side member.

According to the aforementioned configuration, it is possible to reinforce the lower-arm support portion itself by the brace.

INDUSTRIAL APPLICABILITY

As described above, the present invention is advantageously applied to a rear subframe structure provided with a rear subframe including a front cross member extending in the vehicle width direction, and a pair of left and right side members connected to the front cross member and extending in a vehicle front-rear direction; and a vehicle-body mounting portion formed on both ends of the front cross member in the vehicle width direction. 

The invention claimed is:
 1. A rear subframe structure, comprising a rear subframe including: a front cross member extending in a vehicle width direction, a left side member connected to the front cross member and extending in a vehicle front-rear direction; and a right side member connected to the front cross member and extending in the vehicle front-rear direction; a vehicle-body mounting portion formed on both ends of the front cross member in the vehicle width direction; a tunnel portion formed in a middle of a lower portion of the front cross member through which a propeller shaft extends; and a brace extending in the vehicle width direction below the tunnel portion, and including a tunnel-portion mounting portion on left and right ends thereof, wherein the brace includes a middle downwardly bulging portion bulging downwardly while avoiding the propeller shaft, and an upwardly bulging portion continued outwardly of the middle downwardly bulging portion in the vehicle width direction and bulging upwardly while avoiding an exhaust pipe, and an inflection point between the middle downwardly bulging portion and the upwardly bulging portion is substantially located on an imaginary line linearly connecting the left and right tunnel-portion mounting portions in the vehicle width direction.
 2. The rear subframe structure according to claim 1, wherein a differential mount portion for supporting a differential mount bush is formed on the upwardly bulging portion.
 3. The rear subframe structure according to claim 1, wherein the left side member is a left upper side member and the right side member is a right upper side member, the rear subframe further includes a rear cross member extending in the vehicle width direction on a rear side of the front cross member, and a left lower side member and a right lower side member each of which extends in the vehicle front-rear direction on a lower side of the left upper side member and right upper side member, respectively, and the brace is connected to the left and right lower side members at a position where the brace overlaps, in a bottom view, a lower-arm support portion constituted by the lower portion of the front cross member, and a pillar portion formed on a rear side of the lower portion of the front cross member between an upper portion of the front cross member and the left and right lower side members, or between the left and right upper side members and the left and right lower side members. 